This application is related to a co-pending application that bears Motorola docket number CR 97-133 and U.S. Ser. No. 09/144,686, entitled "MAGNETIC RANDOM ACCESS MEMORY AND FABRICATING METHOD THEREOF," filed on Aug. 31, 1998, assigned to the same assignee and incorporated herein by this reference, co-pending application that bears Motorola docket number CR 97-158 and U.S. Ser. No. 08/986,764, entitled "PROCESS OF PATTERNING MAGNETIC FILMS" filed on Dec. 8, 1997, assigned to the same assignee and incorporated herein by this reference, copending application that bears Motorola docket number CR 99-001 and U.S. Ser. No. 09/356,864, entitled "MAGNETIC ELEMENT WITH IMPROVED FIELD RESPONSE AND FABRICATING METHOD THEREOF", filed Jul. 19, 1999, assigned to the same assignee and incorporated herein by this reference and issued U.S. Pat. No. 5,768,181, entitled "MAGNETIC DEVICE HAVING MULTI-LAYER WITH INSULATING AND CONDUCTIVE LAYERS", issued Jun. 16, 1998, assigned to the same assignee and incorporated herein by.
Typically, a magnetic memory element, such as a magnetic tunnel junction memory element, has a structure that includes ferromagnetic layers separated by a non-magnetic spacer layer. Information is stored as directions of magnetization vectors in the magnetic layers. Magnetic vectors in one magnetic layer, for instance, are magnetically fixed or pinned in the operating magnetic field range, while the magnetization direction of the other magnetic layer is free to switch between the same and opposite directions that are called "parallel" and "antiparallel" states, respectively. In response to parallel and antiparallel states, the magnetic memory element represents two different resistances. The resistance has minimum and maximum values when the magnetization vectors of the two magnetic layers point in substantially the same and opposite directions, respectively. Accordingly, a detection of change in resistance allows a device, such as an MRAM device, to provide information stored in the magnetic memory element. The difference between the minimum and maximum resistance values, divided by the minimum resistance is known as the magnetoresistance ratio (MR).
A MRAM device integrates magnetic elements, more particularly magnetic memory elements, and other circuits, for example, a control circuit for magnetic memory elements, comparators for detecting states in a magnetic memory element, input/output circuits, etc. These circuits are fabricated in the process of CMOS (complementary metal-oxide semiconductor) technology in order to lower the power consumption of the device.
In addition, magnetic elements structurally include very thin layers, some of which are tens of angstroms thick. The resistance versus magnetic field response of the magnetic elements is affected by the surface morphology of the thin layers. In order for a magnetic element to operate as a memory cell, it needs to have at least two resistance states when it is at resting state, or, when there is no magnetic field applied to it. This requirement on the magnetic elements is equivalent to having a nearly centered resistance versus magnetic field response. The presence of topological positive coupling and pin-hole coupling must be corrected to yield centered resistance.
During typical MTJ magnetic element fabrication, such as MRAM memory element fabrication, which includes metal films grown by sputter deposition, evaporation, or epitaxy techniques, the film surfaces are not absolutely flat but instead exhibit surface or interface waviness. This waviness of the surfaces and/or interfaces of the ferromagnetic layers is the cause of magnetic coupling between the free ferromagnetic layer and the other ferromagnetic layers, such as the fixed layer or pinned layer, which is known as topological coupling or Neel's orange peel coupling. Such coupling is typically undesirable in magnetic elements because it creates an offset in the response of the free layer to an external magnetic field. In addition, during typical spin valve magnetic element fabrication, electronic exchange coupling is present. Compensation for this type of coupling, as well as the presence of any other coupling effects commonly found in MTJ and spin valve elements must be compensated for to produce a centered resistance, and thus operation of the device in dual states.
Further, two kinds of offset in MRAM memory cell switching fields are commonly present. The first kind, as previously discussed, is the ferromagnetic coupling or positive coupling and is caused by topology-related magneto-static coupling and results in only the low resistance memory state being present at zero applied field. The memory cell in effect does not work. At least two memory states are required at zero field for the memory to function. The other kind of cell switching offset is called anti ferromagnetic coupling or negative coupling. It is caused by magneto-static coupling at the ends of the memory cell with cell length to width ratio of equal or greater than 1. Its effect is to have only the high resistance memory state present at zero applied field. Again the memory does not work without a reading magnetic field applied. It is preferable to perform the reading without applying a magnetic field caused by current pulse(s) to save power and achieve high speed.
Therefore, it is necessary to produce a device that includes bit end magneto-static fringing fields that cancel the total positive coupling of the structure, thus achieving dual magnetic states in a zero external field.
It is said that the ferromagnetic coupling strength is proportional to surface magnetic charge density and is defined as the inverse of an exponential of the interlayer thickness. As disclosed in U.S. Pat. No. 5,764,567, issued Jun. 9, 1998, and entitled "MAGNETIC TUNNEL JUNCTION DEVICE WITH NONFERROMAGNETIC INTERFACE LAYER FOR IMPROVED MAGNETIC FIELD RESPONSE", by adding a non-magnetic copper layer next to the aluminum oxide tunnel barrier in a magnetic tunnel junction structure, hence increasing the separation between the magnetic layers, reduced ferromagnetic orange peel coupling, or topological coupling, is achieved. However, the addition of the copper layer will lower the MR of the tunnel junction, and thus degrade device performance. In addition, the inclusion of the copper layer will increase the complexity for etching the material.
Accordingly, it is a purpose of the present invention to provide an improved magnetic element having centered resistance response curve with respect to an applied magnetic field, thereby capable of operating in dual states.
It is another purpose of the present invention to provide an improved magnetic element that includes compensation for the existence of ferromagnetic coupling, more particularly ferromagnetic coupling of topological origin or exchange coupling.
It is still a further purpose of the present invention to provide for a magnetic element wherein the bit end demagnetizing fields cancel the total positive coupling of the structure to obtain dual magnetic states in a zero external field
It is a still further purpose of the present invention to provide a method of forming a magnetic element having centered resistance versus field response, thereby capable of operating in dual states.
It is still a further purpose of the present invention to provide a method of forming a magnetic element having centered resistance versus field response which is amenable to high throughput manufacturing.